The invention relates to imaging systems, and more particulary relates to scintillation camera imaging systems.
In a conventional scintillation gamma camera, scintillation event from gamma radiation are individually associated with individual pixels in the image. For example, in a conventional scintillation camera, a particular scintillation event may be detected by location (x, y). The energy of this scintillation event is then measured. When the energy of the scintillation event is quite different from the energy of a gamma ray, the event itself is considered to have a relatively low probability of contributing useful information to the final image and the event is therefore ignored. On the other hand, when the event energy is quite similar to the energy of a gamma ray, it has a relatively high probability of contributing useful information to the finished image and a single count is then associated with location (x, y). The image produced by the scintillation camera is derived from image data which associates a particular number of counts with each pixel in the finished image.
This conventional scintillation camera has the theoretical drawback that the detected location of a scintillation event is influenced by random scatter. The use of energy window-type qualification criteria for the detected scintillation event does not take proper account of the information content inherent in the energy of such events. This is because all events whose energies fall within the energy window are assumed to have equal probabilities of contributing useful information to the final image. This is not so. Two different scintillation events whose energies are dissimilar but are still within the energy window may contain substantially different amounts of useful information.
Furthermore, the attribution of an event to one pixel alone is statistically inaccurate. It is more accurate to attribute an observed scintillation event to a plurality of pixels with individual pixel weights distributed in accordance with the laws of probability.
It has been proposed to assign a weight to a detected scintillation event in accordance with the energy of that event, rather than (a) qualifying and disqualifying events based upon their falling within or outside a predefined energy window, and (b) counting all qualified events identically. This is called weighted acquisition. However, it has not until recently been possible to implement this technique in a conventional scintillation camera. This is because the precision of the energy signal has been too poor for reliable results.
One object of the invention is to provide a device for implementing area-weighted acquisition in an imaging system.
Another object is to provide such a device which takes more accurate account of the energy of a detected scintillation event than do conventional scintillation cameras which qualify events using an energy window.
Still aonther object is to provide such a device which attributes scintillation events to a plurality of pixels in accordance with the laws of probability, i.e. which implements multiple-pixel area-weighted acquisition.
A further object is to provide such a device which is easily programmable to be utilizable with a variety of radioisotope/collimator combinations.
Another object is to provide such a device which can be used to retrofit a conventional scintillation camera (provided that the camera has a suitable energy precision) to implement area-weighted acquisition in a convenient manner which still permits the camera to operate in a conventional non-weighted acquisition mode if desired.
Still a further object is, in general, to improve on the prior art.